Separation of thiophenols and tar acids



Get. 16, 1956 M. B. NEU-WORTH 2,7673%0 SEPARATION OF THIOPHEIfIOLSAND TAR ACIDS Filed Aug. 7, 1953 46g MAKEUP l6 AQUEOUS V "ETHANOL "ETHAmL A 7459 I 36 1 a v TAR" 26- a a '50 Y 74- 2 I Q FEED- E 2 K f L; E k 4 3 m I\ Q R E a Q E v Q Q 12 m g 2 m 2 E- Q 4 m o r 9 Q b E {s 32 b 2 a 3 THIOPHENOLS 31- A TAR 24 ACIDS .IF 22 v 6'8 v INVENTOR NAPHTHA MARTIN B. NEUWORTH United States Patent SEPARATION or THIOPHENOLS AND TAR ACIDS Martin B. Neuworth, Pittsburgh, Pa., assignor to Pittsburgh Consolidation Coal Company, Pittsburgh, Pa., a corporation of Pennsylvania Application August 7, 1953, Serial No. 372,972

Claims. (Cl. 260-627) This invention relates to the art of refining tar acids, and more particularly, to the removal of thiophenols from tar acids.

The two principal commercial sources of tar acids are coke-oven tar and petroleum distillates resulting from oil cracking processes. The conventional method of recovering tar acids from either source is to extract the tar acids with aqueous caustic solution to produce water soluble tar acid salts. The latter are separated from the source material by decantation and reconverted to tar acids on reaction with mineral acids. Other sources of tar acids include tar from low temperature carbonization of coal and shale oil distillates. These sources, however, are still largely undeveloped in this country.

The extraction of tar acids by means of aqueous caustic solution is accompanied, naturally, by the extraction of thiophenols since the latter are even stronger acids than the phenols themselves. The quantity of thiophenols in the original source material varies widely, being sometimes as little as one percent by weight of the phenols and ranging as high as twentyfive percent and above. Their presence in the extracted tar acids is undesirable for many industrial applications.

Many schemes have been proposed for the removal of the thiophenols from the caustic extracted tar acids. The most successful ones, are based upon the ease of oxidation of the thiophenols to disulfides. It is difiicult to keep thiophenols free of disulfid-es since normal handling will expose them to air and result in at least partial oxidation. Accordingly the proposed schemes, in view of this behavior, have resorted to deliberate oxidation with air to completely convert the thiophenols to disulfides. The latter are readily separable from the tar acids because of their insolubility in an aqueous medium.

The general method of oxidation to disulfides has three disadvantages; firstly, destruction of a significant quantity of the valuable tar acids results from the oxidation; secondly, redistillation of the tar acids causes a reversion of any remaining dis-ulfides to thiophenols; and thirdly, the 'thiophenol content of the tar acids is still not reduced sufliciently for some commercial applications.

Analysis of a typical commercial product of petroleum cresylics (i. e. tar acids boiling below 230 C.) that were recovered by caustic extraction and oxidized to remove thiophenols shows 97.7% by weight of tar acids; 1% by weight of neutral oil; 1% by Weight of sulfur compounds (total); and 0.3% by weight of tar bases. The sulfur is, of course, present in organic sulfur compounds, principally unoxidized or reconverted thiophenols, and disulfides resulting from oxidation of the thiophenols. For many industrial resin applications, 1% by weight of sulfur compounds is too high.

In accordance with the present invention, I have provided a method of removing thiophenols from tar acids that are substantially free of neutral oil. The method comprises contacting the tar acids with aqueous methanol and a low boiling paraftinic naphtha fraction in a continuous countercurrent extraction zone.

2,767,220 Patented Oct. 16, 1956 In copen'ding application Serial Number 184,474, filed September 12, 1950, now Patent Number 2,666,796, of which I am one of the joint applicants, there is described a method of recovering tar acids from tar acid oils by solvent extractive treatment with aqueous methanol and a paratfinic naphtha. We pointed out in that application that a substantial part of the organic sulfur compounds was recovered in the neutral oil fraction. Presumably, the sulfur compounds thus recovered were neutral in character. Because the thiophenols are stronger acids than the phenols, one would expect the former to remain in the polar solvent, namely, aqueous methanol. However, I have found that the reverse is true. The less acidic phenols remain in the polar solvent (aqueous methanol) and the more acidic thiophenols are recovered in the non-polar solvent (hexane). Furthermore the separation resulting from such extractive treatment is extremely effective. Tar acids of high purity can be recovered in virtually quantitative yields.

In the process of my invention, the feedstock consists of tar acids from which substantially all the neutral oil has been separated. This feedstock generally but not necessarily has a boiling range from 160 to 300 C., or some part thereof, particularly the fraction boiling up to 230 C. The organic sulfur contaminants comprising principally thiophenols (i. e. thiophenol itself, thiocresols, thioxylenols, etc.) may be present in amounts from about 0.5 to 25% by weight of the feedstock.

The tar acid feedstock is fed into a continuous, countercurrent, double solvent, extraction zone. Aqueous methanol solution is fed into one end of the zone and a low boiling, essentially parafiinic naphtha fraction is fed into the other end of the zone. The aqueous methanol passes through the Zone dissolving substantially all the tar acids. The naphtha passes countercurrently through the zone dissolving the thiophenols and any residual neutral oil. The tar acids may then be readily recovered from the aqueous methanol by stripping the solvent; and similarly, the thiophenols may be recovered from the naphtha solution for disposal as waste or for commercial use depending on the quantity.

*In the present process, it is necessary to employ aqueous methanol solution containing from about 40 to 90 percent by weight of methanol, preferably from 55 to percent by weight of methanol.

In concentrations below about 40 percent methanol, recovery of tar acids becomes too low to be practical. Above about percent methanol concentration, the methanolsolution dissolves the thiophenols so that the extracted tar acids remain contaminated to an undesirable extent.

The process of this invention is further critically conditioned by the characteristics of the naphtha solvent. It must be essentially parafiinic in character. Such solvents may be obtained from the distillation of parafiinic petroleum stocks. Its boiling range should be 60 to 130 C., but preferably 60 to C., in order to facilitate the subsequent stripping of the naphtha solvent from the naphtha extract. And finally, the naphtha density should be less than 0.80 and preferably less than 0.75 to ensure a gravity dilference between the two phases in the extraction column sufficient to effect a ready separation of the phases. The hexane cut of paraffinic naphtha combines all these critical properties and accordingly is preferred as the non-polar solvent. 7

For a better understanding of my invention, its objects and advantages, reference should be had to the drawing which is a diagrammatic illustration of apparatus adapted for the practice of the preferred embodiment of this invention.

Referring to the drawing, tar acid feedstock as previously defined is pumped continuously from a storage tank 10 through a pipeline 12 into a continuous countercu'rferred embodiment of a vertical center --feed extraction column 14. The extraction column may be of any convenient design capable of providing a sufiicient number of theoretical extraction stages to eifect the desired separation of fat acids. A conventional packed .tower' eral, the feedstock is preferably introduced at a point above the geometric center of any given extraction column.

Aqueous methanol solution is fed continuously from.

an aqueous methanol storage tank 16 through pipeline 18 into the top of the extraction column 14. Naphtha is fed continuously from the naphtha storage tank20 through a pipeline 22 into the base of the extraction column 14. I V V 7 Since the density of the aqueous methanol solution exceeds the density of the naphtha, the aqueous methanol solution descends through the column, dissolving tar a'cids; 'while the lighter naphtha passes countercurrently upward through the column, dissolving the thiophenols contained in the tar acid feedstock. Column throughput and contact time are dependent upon the column design.

For every volume of tar acid feedstock from 0.5 to 5.0 volumes of aqueous .methanol and from 0.5 to 5.0 volumes of naphtha should be employed, whenever both high tar acid recovery and high tar acid purity are de sired. These flow ratios are therefore preferred. The ratio of aqueous methanol to naphtha should be controlled according to the solvent which is selected as the continuous phase. When naphtha is employed as the continuous phase, it is necessary in order to obtain high yields of a high purity product to regulate the solvent ratio so that the volume of aqueous methanol is from 0.25 to 4.0 times the volume of naphtha. When aqueous methanol is employed as the continuous phase, it is necessary, again in order to obtain high yields of a high purity product to regulate the solvent ratio so that the volume of aqueous methanol is from 0.5 to 2.0 times the volume of naphtha. p

It may be desirable to add a portion of the naphtha solvent to the tar acid feedstock, especially when a high viscosity tar acid fraction is beingtreated, i. e. one having a high end boiling point. When such technique is employed, the naphtha so added should be considered as solvent for the purpose of determining solvent-to-feed and solvent-to-solvent ratios.

While the method of the present invention is relatively independent of the temperature at which the column is operated, it is preferred to operate the extraction column within the range of 60 to 120 F. The increased viscosity of the tar acid feedstock below this range introduces col-.

umn operationdifliculties, while the increasing solubility of the thiophenols in the aqueous methanol solvent at higher temperatures decreases the purity of the recovered tar acids. If necessary, the extraction column may be heated or cooled in any convenient manner.

Aqueous methanol extract, containing purified .tar acids, is withdrawn continuously from the bottom of extraction column 14 through a pipeline 24 and fed into a distillation column 26 for the separation of the methanol.

solvent from the water and purified. tar acids both of.

which leave the still as bottoms throughpipeline 28 and pass into a phase .separation tank 30. Since the solu-- bility of tar acids in water decreases with reduction in temperature, a cooler 32 may be placed in line.28 to cool the water and tar acids passing through line 28 and thereby to decrease the proportion of residualtar acids in the aqueous layer in phase separator 30. Purified taracids,

being virtually immiscible in water, separate from-the aqueous layer in phase separator and are withdrawn either continuously or intermittently as product through pipeline 34. The aqueous phase from the phase separator 30 is withdrawn through'pipeline 36 and sent'to the aqueous methanol storage tank 16 for recirculation.

Anhydrous meflianol passes overhead from distillation tower 26 through pipeline 38 to a reflux condenser 40. Condensed anhydrous methanol leaves the reflux condenser 40 and passes through pipeline 42 to the aqueous methanol storage tank 16 for recirculation. "A portion of the condensed methanol is returned through pipe-' line 44 to the top of distillation column 26 as reflux.

It should be'pointed out that in the preparation of the aqueousrmethanol solution in the storage tank 16, caution should be exercised if the solution is prepared and its composition regulated by specific gravity measurement. The recirculated methanol is saturated 'with naphtha and this fact must be considered in determining I reflux condenser 54. A portion of the condensed naphtha may be circulated through pipeline 56 as reflux for the distillation column 50. The remainder of the naphtha is returned to the naphtha storage tank 20 through pipeline 58 for recirculation. Thiophenols leave the still as the bottom product through pipeline 60. A cooler 62 may be inserted in the exit pipeline to cool the sulphur product.

In the following table are tabulated the results from the application of my process to two diflerent'mixtures of tar acids. In Run A the feedstock was a commercially available product consisting of petroleum cresylics, i. e. tar acids, having a boiling range of 19 l243 C. In Run B the feedstock consisted of a synthetic mixture of thiocresol and tar acids having a boiling range of to 225 C.

A one-inch diameter, eight-feet long, center feed, countercurrent extraction column was employed and con-, tained in its contacting zone 29 settling stages alternately disposed with 28 agitation stages. The column was op: erated at a temperature of 25 C. The continuous solvent phase was naphtha. i

Run Number A V B Composition of Feedstock (percent by Weight):

Tar Acids 9G. 2 82. 3 Thionheunls 0. 8 l7. 7 Disulfides l. 6 Neutral Oil 1.4 O 04 Feed Rates, ml./min.: Feedstock 5. 0 5. 0 Aqueous Methanol 1 10. 0 10. 0 HPXHT19 15. 0 15. 0 Tar Acid Recovery (Wt. Percent Solvent Free) 99. 6 99. 7 Extract Composition (Wt. Percent Solvent Free):

Neutral oil 0. 04 0. 01 Thicmh punk 0. 0025 U. 05. Disulfides 0. 024 0.06 Tar Acids 99. 93 99.88

1 The aqueous methanol solvent consisted of 70% by weight of CHaOH- audthe balance Water.

Examination of the above table (Run A) shows that 99.6 percent of the tar acids were recovered withla purity of 99.9%. The thiophenol content was reduced from 0.8% to 0.0025%' and the disulfides from 1.6% to 0.024%. With reference to Run B,the concentrationof thiocresol represents an extreme in thiophenol content, which can be encountered in the raw alkaline extract from a cracked petroleum fraction. The recovery of tar acids was 99.7% accompanied by a purity of 99.9%..

The thiocresol content was reduced from 17.7 to 0.05%. Part of the thiocresol in the feed was oxidized by contact with air to disulfides. The disulfide contamination of the extract was 0.06%.

According to the provisions of the Patent Statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A process for separating thiophenols from tar acids that are substantially free of neutral oil which comprises the steps of feeding said tar acids to an extraction zone, feeding an aqueous methanol solution containing about 40 to 90 weight percent methanol and the balance water to one end of said extraction zone, feeding a second solvent consisting of a paraflfinic naphtha fraction boiling within the range of 60 to 130 C. and having a density of less than 0.8 to the other end of said extraction zone, passing said aqueous methanol solution and said naphtha fraction through said extraction zone in countercurrent relation, and recovering the aqueous methanol extract containing tar acids.

2. A process for separating thiophenols from tar acids that are substantially free of neutral oil which comprises the steps of feeding said tar acids to a vertical extraction zone at a point located between the ends thereof, feeding an aqueous methanol solution containing about 40 to 90 Weight percent methanol and the balance water to the top of said extraction zone, feeding a second solvent consisting of a parafiinic naphtha fraction boiling Within the range of 60 to 130 C. and having a density of less than 0.8 to the bottom of said extraction zone, passing said aqueous methanol solution and said naphtha raction through said vertical extraction zone in countercurrent relation, and recovering aqueous methanol extract containing tar acids from the bottom of said vertical extraction zone.

3. The process of claim 2 in which the aqueous methanol solution contains 55 to 75 weight percent methanol and the balance water.

4. The process of claim 2 in which the tar acids have a high end boiling point of about 230 C.

5. A process for separating thiophenols and tar acids which comprises the steps of feeding a mixture consisting essentially of tar acids and thiophenols to a vertical extraction zone at a point located between the ends thereof, feeding an aqueous methanol solution containing to weight percent methanol and the balance water to the top of said vertical extraction zone, feeding a second solvent consisting of a paraffinic naphtha fraction boiling within the range of 60 to C. and having a density less than 0.8 to the bottom of said vertical extraction zone, circulating said aqueous methanol solution downwardly and said naphtha fraction upwardly through said vertical extraction Zone in countercurrent relation, regulating the rate of withdrawal of said solvents from said extraction zone so that the naphtha phase is the continuous phase, regulating the feed rate so that at least 0.5 and not more than 5.0 volumes of said aqueous methanol solution and at least 0.5 and not more than 5.0 volumes of said naphtha are fed to said extraction zone for every volume of said tar acid mixture fed to said extraction zone, further regulating the feed rates so that the volume of aqueous methanol solution is at least 0.25 but not more than 4.0 times the volume of naphtha fed to said extraction zone, and separately recovering the aqueous methanol extract and the naphtha extract.

6. The process of claim 5 in which said mixture of tar acids and thiophenols contains from 0.5 to 25 percent by Weight of the thiophenols.

7. The process of claim 5 in which the naphtha solvent is a parafiinic naphtha boiling within the range of 60 to 100 C.

8. The process of claim 5 in which the naphtha solvent is a hexane cut of petroleum naphtha.

9. The process of claim 5 in which said mixture of tar acids and thiophenols was derived from a petroleum distillate fraction by caustic extraction thereof.

10. The process of claim 5 in which said mixture of tar acids and thiophenols boils above C. and below 300 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,334,691 Andersen Nov. 23, 1943 2,488,479 Schindler Nov. 15, 1949 2,666,796 Gorin et a1. Jan. 19, 1954 

1. A PROCESS FOR SEPARATING THIOPHENOLS FROM TAR ACIDS THAT ARE SUBSTANTIALLY FREE OF NEUTRAL OIL WHICH COMPRISES THE STEPS OF FEEDING SAID TAR ACIDS TO AN EXTRACTION ZONE, FEEDING AN AQUEOUS METHANOL SOLUTION CONTAINING ABOUT 40 TO 90 WEIGHT PERCENT METHANOL AND THE BALANCE WATER TO ONE END OF SAID EXTRACTION ZONE, FEEDING A SECOND SOLVENT CONSISTING OF A PARAFFINIC NAPHTHA FRACTION BOILING WITHIN THE RANGE OF 60* TO 130* C. AND HAVING A DENSITY OF LESS THAN 0.8 TO THE OTHER END OF THE SAID EXTRACTION ZONE, PASSING SAID AQUEOUS METHANOL SOLUTION AND SAID NAPHTHA FRACTION THROUGH SAID EXTRACTION ZONE IN COUNTERCURRENT RELATION, AND RECOVERING THE AQUEOUS METHANOL EXTRACT CONTAINING TAR ACIDS. 